In the typical passenger vehicle, the support for the front passenger seats consists of a pair of steel seat rails which are mounted to the floorboard region of the vehicle body and include an inner seat rail disposed adjacent the longitudinal center axis of the vehicle and an outer seat rail welded to a corresponding side door sill member. However, such a weld connection for the outer seat rail is only possible where the materials selected for the door sill member and the outer seat rail are capable of being welded to one another.
A current trend in motor vehicle design has been to reduce the overall weight of the vehicle by using extruded light-alloy sections in place of traditional welded together sheet metal stampings for various hollow section, load bearing members of the vehicle bodywork. For example, European Patent Document No. 0 229 591 discloses side door sill members which are fabricated from light-alloy extruded sections. In such a design, however, it is not possible to weld the seat rail to the alloy door sill member since the seat rail must consist of steel in order to satisfy the requirements of material thickness, strength, and stiffness and thus cannot be welded to a dissimilar material such as light-alloy. Another disadvantage of the above-described design is that it is difficult to combine the two steel seat rails into an alloy underframe in order to simplify assembly.
German Patent Document DE-C 2 916 562 discloses a similar construction wherein an underframe for the front passenger seat is fastened at its front and rear to adjacent front and rear cross members which are formed integral with the floor panel. This design, however, is disadvantageous since the leg room for the front passengers is restricted by the introduction of the forward cross member disposed in front of the underframe. Also, the relatively thin floor panel cannot withstand the forces acting on the seat rails in the event of a front or rear collision but rather tears unless special reinforcements are provided.
Accordingly, there is a definite need in the art for an improved connection between a steel outer seat rail and a adjacently disposed extruded light metal side door sill member which overcomes the problems of the prior art.